Technical Field
[0001] The present invention relates to a high-performance vehicle steering apparatus that
obtains a desired steering torque based on a torsional angle of a torsion bar and
so on, and maintains the desired steering torque without being affected by a road
surface state and changes of mechanical system characteristics due to aging.
Background Art
[0002] An electric power steering apparatus (EPS) which is one of vehicle steering apparatuses
provides a steering system of a vehicle with an assist torque (a steering assist torque)
by means of a rotational torque of a motor, and applies a driving force of the motor
which is controlled by using an electric power supplied from an inverter as the assist
torque to a steering shaft or a rack shaft by means of a transmission mechanism including
a reduction mechanism. In order to accurately generate the assist torque, such a conventional
electric power steering apparatus performs a feed-back control of a motor current.
The feed-back control adjusts a voltage supplied to the motor so that a difference
between a steering assist command value (a current command value) and a detected motor
current value becomes small, and the adjustment of the voltage supplied to the motor
is generally performed by an adjustment of a duty ratio of a pulse width modulation
(PWM) control.
[0003] A general configuration of the conventional electric power steering apparatus will
be described with reference to FIG. 1. As shown in FIG.1, a column shaft (a steering
shaft or a handle shaft) 2 connected to a handle (a steering wheel) 1 is connected
to steered wheels 8L and 8R through a reduction mechanism 3, universal joints 4a and
4b, a rack-and-pinion mechanism 5, and tie rods 6a and 6b, further via hub units 7a
and 7b. In addition, a torque sensor 10 for detecting a steering torque Ts of the
handle 1 and a steering angle sensor 14 for detecting a steering angle θh are provided
in the column shaft 2 having a torsion bar, and a motor 20 for assisting a steering
force of the handle 1 is connected to the column shaft 2 through the reduction mechanism
3. The electric power is supplied to a control unit (ECU) 30 for controlling the electric
power steering apparatus from a battery 13, and an ignition key signal is inputted
into the control unit 30 through an ignition key 11. The control unit 30 calculates
a current command value of an assist command (a steering assist command) based on
the steering torque Ts detected by the torque sensor 10 and a vehicle speed Vs detected
by a vehicle speed sensor 12, and controls a current supplied to the motor 20 for
the electric power steering apparatus (EPS) by means of a voltage control command
value Vref obtained by performing compensation or the like to the current command
value.
[0004] A controller area network (CAN) 40 exchanging various information of a vehicle is
connected to the control unit 30, and it is possible to receive the vehicle speed
Vs from the CAN 40. Further, it is also possible to connect a non-CAN 41 exchanging
a communication, analog/digital signals, a radio wave or the like except for the CAN
40 to the control unit 30.
[0005] The control unit 30 mainly comprises a central processing unit (CPU) (including a
micro controller unit (MCU), a micro processor unit (MPU) and so on), and general
functions performed by programs within the CPU are shown in FIG.2.
[0006] Functions and operations of the control unit 30 will be described with reference
to FIG.2. As shown in FIG.2, the steering torque Ts detected by the torque sensor
10 and the vehicle speed Vs detected by the vehicle speed sensor 12 (or from the CAN
40) are inputted into a current command value calculating section 31. The current
command value calculating section 31 calculates the current command value Iref1 that
is a control target value of a current supplied to the motor 20 based on the inputted
steering torque Ts and vehicle speed Vs and by using an assist map or the like. The
current command value Iref1 is inputted into a current limiting section 33 through
an adding section 32A. A current command value Irefm whose maximum current is limited
is inputted into a subtracting section 32B, and a deviation I (= Irefm - Im) between
the current command value Irefm and a motor current Im being fed-back is calculated.
The deviation I is inputted into a proportional integral (PI)-control section 35 for
improving a characteristic of the steering operation. The voltage control command
value Vref whose characteristic is improved by the PI-control section 35 is inputted
into a PWM-control section 36. Furthermore, the motor 20 is PWM-driven through an
inverter 37. The motor current Im of the motor 20 is detected by a motor current detector
38 and is fed-back to the subtracting section 32B.
[0007] A compensation signal CM from a compensation signal generating section 34 is added
to the adding section 32A, and a characteristic compensation of the steering system
is performed by the addition of the compensation signal CM so as to improve a convergence,
an inertia characteristic and so on. The compensation signal generating section 34
adds a self-aligning torque (SAT) 343 and an inertia 342 at an adding section 344,
further adds the added result at the adding section 344 with a convergence 341 at
an adding section 345, and then outputs the added result at the adding section 345
as the compensation signal CM.
[0008] In such a conventional assist control of the electric power steering apparatus, the
steering torque applied by the manual input of the driver is detected as the torsional
torque of the torsion bar by the torque sensor, and the motor current is controlled
as the assist current depending on mainly the detected steering torque. However, in
this method, different steering torques are generated depending on the steering angle
due to the difference of the road surface state (for example, a tilt of the road surface).
Moreover, even variations of the motor output characteristic due to the long-term
use of the motor are affected to the steering torque.
[0009] In order to resolve the above problems, the electric power steering apparatus disclosed
in, for example, Japanese Patent No.
5208894 (Patent Document 1) is proposed. The electric power steering apparatus of Patent
Document 1 sets the target value of the steering torque based on a relationship (a
steering reaction force characteristic map) between the steering angle and the steering
torque which is determined based on a relationship between the steering angle or the
steering torque and a tactile amount in order to apply the appropriate steering torque
based on the tactile characteristic of the driver.
The List of Prior Art Documents
Patent Documents
[0010] Patent Document 1: Japanese Patent No.
5208894 B2
Summary of the Invention
Problems to be Solved by the Invention
[0011] However, in the electric power steering apparatus of Patent Document 1, it is required
that the steering reaction force characteristic map is preliminarily obtained. Since
the control is performed based on the deviation between the target value of the steering
torque and the detected steering torque, the affection to the steering torque will
still be remained.
[0012] The present invention has been developed in view of the above-described circumstances,
and an object of the present invention is to provide a vehicle steering apparatus
that easily obtains equivalent steering torques to the steering angle and so on without
being affected by a road surface state and changes of mechanical characteristics of
a steering system due to aging.
Means for Solving the Problems
[0013] The present invention relates to a vehicle steering apparatus that comprises a torsion
bar having any spring constant and a sensor to detect a torsional angle of the torsion
bar, and assist-controls a steering system by driving and controlling a motor, the
above-described object of the present invention is achieved by that: comprising a
target steering torque generating section to generate a target steering torque, a
converting section to convert the target steering torque into a target torsional angle,
and a torsional angle control section to calculate a motor current command value so
as to follow-up the torsional angle to the target torsional angle, wherein the target
steering torque generating section comprises an offset correcting section to obtain
a first torque signal from a characteristic depending on a steering angle which is
set based on an offset value of a steering torque and outputs the first torque signal
as the target steering torque, and wherein the vehicle steering apparatus drives and
controls the motor based on the motor current command value.
[0014] The above-described object of the present invention is efficiently achieved by that:
wherein the offset correcting section comprises an offset correction calculating section
to calculate a basic torque signal depending on a steering state and the steering
angle and outputs the basic torque signal which has a hysteresis characteristic whose
value is saturated to a setting value in a right-turning steering and a setting value
in a left-turning steering, as the first torque signal; or wherein the offset correction
calculating section has a hysteresis characteristic whose width is larger than the
offset value; or wherein the offset correcting section further comprises a vehicle
speed sensitive gain section to calculate the first torque signal by multiplying the
basic torque signal by a vehicle speed sensitive gain; or wherein the vehicle speed
sensitive gain has a characteristic that a value of the vehicle speed sensitive gain
becomes smaller when a vehicle speed is higher; or wherein the target steering torque
generating section further comprises a basic map section to obtain a second torque
signal from the steering angle and the vehicle speed using a basic map, and a damper
calculating section to calculate a third torque signal based on angular velocity information
using a damper gain map which is sensitive to the vehicle speed, and calculates the
target steering torque from the first torque signal and at least one of the second
torque signal and the third torque signal; or wherein the basic map is sensitive to
the vehicle speed and has a characteristic that the second torque signal is zero when
the vehicle speed is zero; or wherein the target steering torque generating section
further comprises a phase compensating section which is disposed at a previous stage
or a subsequent stage of the basic map section and performs a phase compensation,
and obtains the second torque signal from the steering angle and the vehicle speed
via the basic map section and the phase compensating section.
Effects of the Invention
[0015] According to the vehicle steering apparatus of the present invention, by performing
a control to the target torsional angle obtained based on the target steering torque
which is generated at the target steering generating section, the torsional angle
can be operated so as to follow-up the target torsional angle and the desired steering
torque based on the steering feeling of the driver can be obtained.
[0016] Further, by the operation of the offset correcting section, the occurrence of the
unintended assist of the driver due to the offset value of the steering torque can
be suppressed and the steering operation can be stabilized when the characteristic
of the basic map section is not changed depending on the steering angle, for example
in a static steering (the vehicle speed is 0 [km/h]) state as shown in FIG.6.
Brief Description of the Drawings
[0017] In the accompanying drawings:
FIG.1 is a configuration diagram illustrating a general outline of a conventional
electric power steering apparatus (EPS);
FIG.2 is a block diagram showing a configuration example of a control unit (ECU) of
the electric power steering apparatus;
FIG.3 is a structural diagram showing an installation example of an EPS steering system
and various sensors;
FIG.4 is a block diagram showing a configuration example of the present invention
(the first embodiment);
FIG.5 is a block diagram showing a configuration example of a target steering torque
generating section (the first embodiment);
FIGs.6A and 6B are a diagram showing a characteristic example of a basic map;
FIG.7 is a diagram showing a characteristic example of a damper gain map;
FIG.8 is a block diagram showing a configuration example of an offset correcting section;
FIG.9 is a diagram showing a characteristic example of the offset correcting section;
FIG.10 is a diagram showing a characteristic example of a vehicle speed sensitive
gain;
FIG.11 is a block diagram showing a configuration example of a torsional angle control
section;
FIG.12 is a diagram showing a setting example of upper and lower limit values at an
output limiting section;
FIG.13 is a flowchart showing an operation example of the present invention (the first
embodiment);
FIG.14 is a flowchart showing an operation example of the target steering torque generating
section (the first embodiment);
FIG.15 is a flowchart showing an operation example of the torsional angle control
section;
FIGs.16A and 16B are a graph showing an example of time response of a steering angle
and a steering torque when the correction by the offset correcting section is not
performed in a simulation showing an effect of the offset correcting section;
FIGs.17A and 17B are a graph showing an example of time response of the steering angle
and the steering torque when the correction by the offset correcting section is performed
in the simulation showing an effect of the offset correcting section;
FIG.I8 is a flowchart showing an operation example of the target steering torque generating
section (the second embodiment);
FIG.19 is a block diagram showing a configuration example of the present invention
(the third embodiment);
FIGs.20A and 20B are a block diagram showing an insertion example of a phase compensating
section;
FIG.21 is a configuration diagram illustrating a general outline of a steer-by-wire
system (SBW system);
FIG.22 is a block diagram showing a configuration example of the present invention
(the fourth embodiment);
FIG.23 is a block diagram showing a configuration example of a target steering angle
generating section;
FIG.24 is a block diagram showing a configuration example of a steering angle control
section; and
FIG.25 is a flowchart showing an operation example of the present invention (the fourth
embodiment).
Mode for Carrying Out the Invention
[0018] The present invention is a vehicle steering apparatus to obtain an appropriate steering
torque to a steering angle and so on without being affected by a road surface state,
and obtains a desired steering torque by performing a control so as to follow-up a
torsional angle of a torsion bar or the like to a value depending on the steering
angle and so on.
[0019] Embodiments of the present invention will be described with reference to the accompanying
drawings.
[0020] First, an installation example of various sensors which detect information related
to an electric power steering apparatus (EPS) which is one of the vehicle steering
apparatuses according to the present invention will be described. FIG.3 is a diagram
showing an EPS steering system and an installation example of the various sensors,
and the torsion bar 2A is provided in the column shaft 2. A road surface reaction
force Fr and a road surface information µ are operated to the steered wheels 8L and
8R. An upper-side angle sensor is disposed at a handle side of the column shaft 2
above the torsion bar 2A, and a lower-side angle sensor is disposed at a steered wheel
side of the column shaft 2 below the torsion bar 2A. The upper-side angle sensor detects
a handle angle θ
1 and the lower-side angle sensor detects a column angle θ
2. The steering angle θh is detected by a steering angle sensor disposed at an upper
portion of the column shaft 2. The torsion bar torsional angle Δθ and the torsion
bar torque Tt can be calculated by following Expressions 1 and 2 from a deviation
between the handle angle θ
1 and the column angle θ
2. In the Expression 2, "Kt" is a spring constant of the torsion bar 2A.
[0021] The torsion bar torque Tt can be detected by using the torque sensor disclosed in,
for example, Japanese Unexamined Patent Publication No.
2008-216172 A. In the present embodiment, the torsion bar torque Tt is also treated as the steering
torque Ts.
[0022] Next, the configuration example of the present invention will be described.
[0023] FIG.4 is a block diagram showing a configuration example of the present invention
(the first embodiment), and the handle steering of the driver is assist-controlled
by the motor in an EPS steering system/vehicle system 100. The steering angle θh,
the vehicle speed Vs and a steering state STs which indicates a right-turning or a
left-turning and is outputted from a right-turning/left-turning judging section 500
are inputted into a target steering torque generating section 200 which outputs a
target steering torque Tref. The target steering torque Tref is converted into a target
torsional angle Δθref at a converting section 400. The target torsional angle Δθref,
the torsional angle Δθ of the torsion bar 2A and the motor angular velocity com are
inputted into a torsional angle control section 300. The torsional angle control section
300 calculates a motor current command value Imc so as to follow-up the torsional
angle Δθ to the target torsional angle Δθref and the motor of the EPS is driven by
the motor current command value Imc.
[0024] The right-turning/left-turning judging section 500 judges whether the steering is
the right-turning or the left-turning based on the motor angular velocity ωm, and
outputs the judged result as the steering state STs. That is, in a case that the motor
angular velocity com is a positive value, the right-turning/left-turning judging section
500 judges "right-turning", and in a case that the motor angular velocity com is a
negative value, the right-turning/left-turning judging section 500 judges "left-turning".
Instead of the motor angular velocity com, the velocity calculation to the steering
angle θh, the handle angle θ
1 or the column angle θ
2 is performed, and the calculated angular velocity may be used.
[0025] FIG.5 shows a configuration example of the target steering torque generating section
200 and the target steering torque generating section 200 comprises a basic map section
210, a differential section 220, a damper gain section 230, an offset correcting section
240, a multiplying section 250 and adding sections 251 and 252. The steering angle
θh is inputted into the basic map section 210, the differential section 220 and the
offset correcting section 240. The vehicle speed Vs is inputted into the basic map
section 210, the damper gain section 230 and the offset correcting section 240. The
steering state STs outputted from the right-turning/left-turning judging section 500
is inputted into the offset correcting section 240.
[0026] The basic map section 210 has a basic map and outputs a torque signal (the second
torque signal) Tref_a whose parameter is the vehicle speed Vs using the basic map.
The basic map is adjusted by a tuning. For example, as shown in FIG.6A, the torque
signal Tref_a increases when the magnitude (the absolute value) |θh| of the steering
angle θh increases, is zero when the vehicle speed Vs is 0 [km/h] and increases when
the vehicle speed Vs increases. In FIG.6A, the sign section 211 outputs the sign ("+1"
or "-1") of the steering angle θh to the multiplying section 212, the magnitude of
the torque signal Tref_a is obtained by the basic map from the magnitude of the steering
angle θh, and the torque signal Tref_a is calculated by multiplying the magnitude
of the torque signal Tref_a by the sign of the steering angle θh. As shown in FIG.6B,
the basic map may change the behavior in a case that the steering angle θh is a positive
value or a negative value. The basic map shown in FIGs.6A and 6B is sensitive to the
vehicle speed. However, the basic map may not be sensitive to the vehicle speed. When
the vehicle speed Vs is zero, the torque signal Tref_a may not be zero and have an
infinitesimal value.
[0027] The differential section 220 differentiates the steering angle θh and calculates
a steering angular velocity ωh, and the steering angular velocity ωh is inputted into
the multiplying section 250.
[0028] The damper gain section 230 outputs a damper gain D
G which is multiplied by the steering angular velocity ωh. The steering angular velocity
ωh which is multiplied by the damper gain D
G at the multiplying section 250 is inputted into the adding section 252 as the torque
signal (the third torque signal) Tref_b. The damper gain D
G is obtained by using a vehicle speed sensitive-type damper gain map that the damper
gain section 230 has, depending on the vehicle speed Vs. For example, as shown in
FIG.7, the damper gain map has a characteristic that a value becomes larger when the
vehicle speed Vs is higher. The damper gain map may be variable depending on the steering
angle θh. The damper calculating section comprises the damper gain section 230 and
the multiplying section 250.
[0029] The offset correcting section 240 calculates the torque signal (the first torque
signal) Tref_c to suppress the occurrence of the assist due to the offset value of
the steering torque in the static steering state (the steering when the vehicle speed
is 0 [km/h]). In a case that the driver does not grip the handle and the offset value
is included in the detected steering torque, when the target steering torque is set
to 0 [Nm] in the static steering state, there can be the occurrence of the assist
because the offset value is existed. The characteristic depending on the steering
angle θh is set based on this offset value (hereinafter, referred to as "an offset
countermeasure characteristic"). The torque signal Tref_c is calculated by using the
offset countermeasure characteristic. FIG. 8 shows a configuration example of the
offset correcting section 240, and the offset correcting section 240 comprises an
offset correction calculating section 241 and a vehicle speed sensitive gain section
242.
[0030] The offset correction calculating section 241 defines the offset countermeasure characteristic
as a hysteresis characteristic shown in FIG.9, and calculates the torque signal (the
basic torque signal) Tref_s based on the steering angle θh and the steering state
STs. In FIG.9, a horizontal axis is the steering angle θh [deg], a vertical axis is
the torque signal Tref_s [Nm], "A
hys" is a hysteresis width, the solid line shows the characteristic in a case of the
right-turning steering, and the broken line shows the characteristic in a case of
the left-turning steering. FIG.9 shows an example that the steering direction is changed
from the right-turning steering to the left-turning steering at the steering angle
(+θh2) and the steering direction is changed from the left-turning steering to the
right-turning steering at the steering angle (-θh2). As shown in FIG.9, in a case
of the right-turning steering, the torque signal Tref_s has a constant value A
hys when the steering angle is between "-θh1" and "θh2" and changes with a constant rate
whose gradient "a" = 2A
hys/(θh2 - θh1) when the steering angle is between "-θh2" and "-θh1". In a case of the
left-turning steering, the torque signal Tref_s has a constant value -A
hys which is a negative value of the hysteresis width A
hys when the steering angle is between "θh1" and "-θh2" and changes with the gradient
"a" when the steering angle is between "θh2" and "θh1". In order to suppress the occurrence
of the assist due to the offset value of the steering torque, the value of the hysteresis
width A
sys is set to be larger than the offset value. The offset countermeasure characteristic
may have a hysteresis characteristic which is changed not in a linear manner shown
in FIG.9 but in a curved manner (a nonlinear manner). In FIG.9, the symmetric hysteresis
characteristic is formed between the right-turning steering and the left-turning steering.
A non-symmetric hysteresis characteristic may be used. For example, in a case that
the offset value of the right-turning steering is different from that of the left-turning
steering, the non-symmetric hysteresis characteristic is adopted.
[0031] The vehicle speed sensitive gain section 242 outputs the torque signal Tref_c by
multiplying the torque signal Tref_s by the vehicle speed sensitive gain. The vehicle
speed sensitive gain is set to become smaller when the vehicle speed Vs becomes higher.
For example, as shown in FIG.10, the vehicle speed sensitive gain is set to "1.0"
when the vehicle speed is 0 [km/h] (the vehicle is in a stop state). The vehicle speed
sensitive gain becomes smaller with a constant rate when the vehicle speed Vs becomes
higher. When the vehicle speed Vs becomes Vs1 (for example, 2 [km/h]), the decrease
rate of the vehicle speed sensitive gain is set to a smaller value. When the vehicle
speed Vs becomes Vs2 (for example, 6 [km/h]), the vehicle speed sensitive gain is
set to zero. The value of the vehicle speed sensitive gain when the vehicle speed
Vs is 0 [km/h] may be a value other than "1.0", the number of the portions where the
decrease rate of the vehicle speed sensitive gain is changed may be plural, and the
vehicle speed sensitive gain may be changed not in a linear manner but in a curved
manner (a nonlinear manner).
[0032] Thus, the offset countermeasure characteristic has a hysteresis characteristic by
the offset correction calculating section 241 and is sensitive to the vehicle speed
due to the vehicle sensitive gain section 242. Thereby, the torque signal Tref_c which
reduces the affection due to the offset value is generated and the occurrence of the
assist due to the offset value of the steering torque can be suppressed by the torque
signal Tref_c. Instead of using the vehicle speed sensitive gain section 242, the
hysteresis width A
hys may be variable depending on the vehicle speed Vs and then the offset countermeasure
characteristic may be sensitive to the vehicle speed. In this case, the vehicle speed
sensitive gain section 242 is not needed. The characteristic other than the hysteresis
characteristic may be used as the offset countermeasure characteristic.
[0033] The torque signals Tref_c and Tref_b are added at the adding section 252, the added
torque signal and the torque signal Tref_a are added at the adding section 251 and
the added result is outputted as the target steering torque Tref.
[0034] The steering angular velocity ωh is calculated by differentiating the steering angle
θh and the appropriate low pass filter (LPF) process is performed to the steering
angular velocity ωh for reducing the affection of the noise in the high frequency
region. The processes of the high pass filter (HPF) and the gain may use in place
of those of the differential calculation and the LPF. Further, the steering angular
velocity ωh may be calculated by differentiating not the steering angle θh but the
handle angle θ
1 which is detected by the upper-side angle sensor or the column angle θ
2 which is detected by the lower-side angle sensor and performing the LPF process to
the differentiation result. The motor angular velocity com may be used as the angular
velocity information instead of the steering angle ωh. In this case, the differential
section 220 is not needed.
[0035] The converting section 400 has a characteristic of "-1/Kt" which is sign-inverted
with respect to a reciprocal of the spring constant Kt of the torsion bar 2A, and
converts the target steering torque Tref into the target torsional angle Δθref.
[0036] The torsional angle control section 300 calculates the motor current command value
Imc based on the target torsional angle Δθref, the torsional angle Δθ and the motor
angular velocity com. FIG.11 is a block diagram showing a configuration example of
the torsional angle control section 300, and the torsional angle control section 300
comprises a torsional angle feed-back (FB) compensating section 310, a torsional angular
velocity calculating section 320, a velocity control section 330, a stabilization
compensating section 340, an output limiting section 350, a subtracting section 361
and an adding section 362. The target torsional angle Δθref outputted from the converting
section 400 is addition-inputted into the subtracting section 361, the torsional angle
Δθ is subtraction-inputted into the subtracting section 361 and is inputted into the
torsional angular velocity calculating section 320, and the motor angular velocity
ωm is inputted into the stabilization compensating section 340.
[0037] A deviation Δθ
0 between the target torsional angle Δθref and the torsional angle Δθ is calculated
at a subtracting section 361. The torsional angle FB compensating section 310 multiplies
the deviation Δθ
0 by a compensation value C
FB (a transfer function), and outputs a target torsional angular velocity ωref so as
to follow-up the torsional angle Δθ to the target torsional angle Δθref. The compensation
value C
FB may be a simple gain Kpp or a compensation value which is generally used, such as
a PI-control compensation value. The target torsional angular velocity ωref is inputted
into the velocity control section 330. It is possible to follow-up the torsional angle
Δθ to the target torsional angle Δθref and obtain the desired steering torque by the
torsional angle FB compensating section 310 and the velocity control section 330.
[0038] The torsional angular velocity calculating section 320 calculates the torsional angular
velocity ωt by differentiating the torsional angle Δθ, and the torsional angular velocity
ωt is inputted into the velocity control section 330. A pseudo differential which
uses the HPF and the gain may be used as the differential operation. The torsional
angular velocity ωt may be calculated from other schemes using the torsional angle
Δθ or the schemes not using the torsional angle Δθ and then may be inputted into the
velocity control section 330.
[0039] The velocity control section 330 calculates the motor current command values Imca1
so as to follow-up the torsional angular velocity ωt to the target torsional angular
velocity ωref by a proportional preceding-type PI-control (I-P control). A difference
(ωref - ωt) between the target torsional angular velocity ωref and the torsional angular
velocity ωt is calculated at the subtracting section 333. The difference is integrated
at the integral section 331 having the gain Kvi, and the integral result is addition-inputted
into the subtracting section 334. The torsional angular velocity ωt is also inputted
into the proportional section 332, the proportional process using the gain Kvp is
performed to the torsional angular velocity ωt, and the proportional-calculated result
is subtraction-inputted into the subtracting section 334. As well, the subtracted
result at the subtracting section 334 is outputted as the motor current command value
Imca1. The velocity control section 330 may calculate the motor current command value
Imca1 by not using the I-P control but using the generally used control method such
as the PI-control, a proportional (P) control, a proportional integral derivative
(PID) control, a derivative preceding-type PID control (a PI-D control), a model matching
control or a model reference control.
[0040] The stabilization compensating section 340 has the compensation value Cs (the transfer
function) and calculates the motor current command value Imca2 from the motor angular
velocity com. In order to improve the followability and the external disturbance characteristic,
when the gains of the torsional angle FB compensating section 310 and the velocity
control section 330 increase, the oscillation phenomenon due to the control in the
high frequency region is occurred. As this countermeasure, the transfer function (Cs)
to the motor angular velocity com, which is required for the stabilization, is disposed
in the stabilization compensating section 340. Thereby, the stabilization of the overall
EPS control system can be realized. The primary filter which is set by the gain and
the pseudo differential whose structure is, for example, the primary HPF, is represented
by the following Expression 3 and is used as the transfer function (Cs) of the stabilization
compensating section 340.
[0041] Here, "K
sta" is a gain, "fc" is a cutoff frequency and "s" is a Laplace operator. For example,
the cutoff frequency fc is set to 150 [Hz]. The secondary filter, the fourth order
filter or the like may be used as the transfer function.
[0042] The motor current command value Imca1 from the velocity control section 330 and the
motor current command value Imca2 from the stabilization compensating section 340
are added at the adding section 362, and the added result is outputted as the motor
current command value Imcb.
[0043] The output limiting section 350 limits the upper and lower limit values of the motor
current command value Imcb and outputs the motor current command value Imc. As shown
in FIG.I2, the upper limit value and the lower limit value to the motor current command
value are preliminarily set. The output limiting section 350 outputs the upper limit
value when the inputted motor current command value Imcb is equal to or larger than
the upper limit value, the lower limit value when the inputted motor current command
value Imcb is equal to or smaller than the lower limit value and the motor current
command value Imcb when the inputted motor current command value Imcb is smaller than
the upper limit value and is larger than the lower limit value, as the motor current
command value Imc.
[0044] In such a configuration, the operation example of the present embodiment will be
described with reference to flowcharts of FIG.13 to FIG.I5.
[0045] When the operation is started, the motor angular velocity com is inputted into the
right-turning/left-turning judging section 500, and the right-turning/left-turning
judging section 500 judges whether the steering is the right-turning or the left-turning
based on the sign of the motor angular velocity ωm, and outputs the judged result
as the steering state STs to the target steering torque generating section 200 (Step
S10).
[0046] The target steering torque generating section 200 inputs the steering state STs,
the steering angle θh and the vehicle speed Vs, and generates the target steering
torque Tref (Step S20). The operation example of the target steering torque generating
section 200 will be described with reference to the flowchart of FIG.I4.
[0047] The steering angle θh inputted into the target steering torque generating section
200 is inputted into the basic map section 210, the differential section 220 and the
offset correcting section 240. The steering state STs is inputted into the offset
correcting section 240. The vehicle speed Vs is inputted into the basic map section
210, the damper gain section 230 and the offset correcting section 240 (Step S21).
[0048] The basic map section 210 generates the torque signal Tref_a depending on the steering
angle θh and the vehicle speed Vs by using the basic map as shown in FIG.6A or FIG.6B,
and outputs the torque signal Tref_a to the adding section 251 (Step S22).
[0049] The differential section 220 differentiates the steering angle θh and outputs the
steering angular velocity ωh (Step S23). The damper gain section 230 outputs the damper
gain D
G depending on the vehicle speed Vs by using the damper gain map as shown in FIG.7
(Step S24). The multiplying section 250 calculates the torque signal Tref_b by multiplying
the steering angular velocity ωh by the damper gain D
G, and outputs the torque signal Tref_b to the adding section 252 (Step S25).
[0050] In the offset correcting section 240, the steering angle θh and the steering state
STs are inputted into the offset correction calculating section 241, and the vehicle
speed Vs is inputted into the vehicle speed sensitive gain section 242. The offset
correction calculating section 241 performs the hysteresis correction to the steering
angle θh depending on the steering state STs by using the offset countermeasure characteristic
as shown in FIG.9 (Step S26), generates the torque signal Tref_s and outputs the torque
signal Tref_s to the vehicle speed sensitive gain section 242. The vehicle speed sensitive
gain section 242 determines the vehicle speed sensitive gain depending on the vehicle
speed Vs by using the characteristic as shown in FIG.10, multiplies the torque signal
Tref_s by the vehicle speed sensitive gain and outputs the multiplication result as
the torque signal Tref_c to the adding section 252 (Step S27). The offset countermeasure
characteristic at the offset correction calculating section 241 may define by using
the hysteresis width A
hys, and the steering angles θh1 and θh2, or may define by using the hysteresis width
A
hys and the gradient "a" instead of the steering angles θh1 and θh2.
[0051] The torque signals Tref_b and Tref_c are added at the adding section 252, the added
result and the torque signal Tref_a are added at the adding section 251, and the target
steering torque Tref is calculated (Step S28).
[0052] The target steering torque Tref which is generated at the target steering torque
generating section 200 is inputted into the converting section 400, and is converted
into the target torsional angle Δθref at the converting section 400 (Step S30). The
target torsional angle Δθref is inputted into the torsional angle control section
300.
[0053] The torsional angle control section 300 inputs the target torsional angle Δθref,
the torsional angle Δθ and the motor angular velocity com, and calculates the motor
current command value Imc (Step S40). The operation example of the torsional angle
control section 300 will be described with reference to the flowchart of FIG.15.
[0054] The target torsional angle Δθref which is inputted into the torsional angle control
section 300 is inputted into the subtracting section 361, the torsional angle Δθ is
inputted into the subtracting section 361 and the torsional angular velocity calculating
section 320, and the motor angular velocity ωm is inputted into the stabilization
compensating section 340 (Step S41).
[0055] In the subtracting section 361, the deviation Δθ
0 is calculated by subtracting the torsional angle Δθ from the target torsional angle
Δθref (Step S42). The deviation Δθ
0 is inputted into the torsional angle FB compensating section 310, and the torsional
angle FB compensating section 310 compensates the deviation Δθ
0 by multiplying the deviation Δθ
0 by the compensation value C
FB (Step S43), and outputs the target torsional angular velocity ωref to the velocity
control section 330.
[0056] The torsional angular velocity calculating 320 inputs the torsional angle Δθ, calculates
the torsional angular velocity ωt by differentiating the torsional angle Δθ (Step
S44), and outputs the torsional angular velocity ωt to the velocity control section
330.
[0057] In the velocity control section 330, the difference between the target torsional
angular velocity ωref and the torsional angular velocity ωt is calculated at the subtracting
section 333 and is integrated (Kvi/s) at the integral section 331, and the integral
result is addition-inputted into the subtracting section 334 (Step S45). Further,
a proportional process (Kvp) is performed to the torsional angular velocity ωt at
the proportional section 332, and the proportional result is subtraction-inputted
into the subtracting section 334 (Step S45). The motor current command value Imca1
which is the subtracted result of the subtracting section 334 is outputted from the
subtracting section 334, and is inputted into the adding section 362.
[0058] The stabilization compensating section 340 performs the stabilization compensation
to the inputted motor angular velocity com by using the transfer function Cs which
is represented by the Expression 3 (Step S46), and the motor current command value
Imca2 from the stabilization compensating section 340 is inputted into the adding
section 362.
[0059] The motor current command values Imca1 and Imca2 are added at the adding section
362 (Step S47). The motor current command value Imcb which is the added result is
inputted into the output limiting section 350. The output limiting section 350 limits
the upper and lower limit values of the motor current command value Imcb by using
the preliminarily set upper limit value and the lower limit value (Step S48) and outputs
the limited value as the current command value Imc (Step S49).
[0060] The motor is driven based on the motor current command value Imc outputted from the
torsional angle control section 300, and the current control is performed (Step S50).
[0061] In FIG.13 to FIG.15, the orders of inputting the data, the calculation and so on
are appropriately changeable.
[0062] The effects of the offset correcting section of the present embodiment will be described
based on the simulation results.
[0063] In the simulations, it is assumed that the offset with 0.05 [Nm] is generated to
the steering torque detected at the torsion bar. Further, assuming that the steering
is the static steering, the basic map that the vehicle speed Vs is 0 [km/h] is used.
Therefore, the value of the torque signal Tref_a outputted from the basic map section
210 is 0 [Nm]. The differential section 220 performs the pseudo differential using
the HPF and the gain as the differential operation.
[0064] First, in a case of "without the correction by the offset correcting section", the
simulation results of the time responses of the steering angle and the steering torque
will be described.
[0065] The simulation results are shown in FIGs.16A and 16B. In FIGs.16A and 16B, the horizontal
axis denotes a time [sec]. The vertical axis denotes the steering angle [deg] in FIG.16A
and the steering torque [Nm] in FIG.16B. FIG.16A shows the time response of the steering
angle whose initial value is 0 [deg]. FIG.16B shows the time response of the target
steering torque by a thin line and the time response of the detected steering torque
by a bold line. The target steering torque is started from 0 [Nm] and the steering
torque is started from -0.05 [Nm]. Since the steering torque whose magnitude of the
offset is 0.05 [Nm] is adjusted so as to follow-up the target steering torque 0 [Nm]
by the torsional angle control at the torsional angle control section 300, the time
response is shown in FIG.16B. As a result, the assist due to the offset value of the
steering torque is occurred and the steering angle is varied as shown in FIG.16A.
That is, the steering torque does not become 0.0 [Nm] in a no-grip state because of
existing the offset value, and the torsional angle control serves so as to follow-up
the torsional angle to the target torsional angle. Thereby, it is estimated that the
variation of the steering angle is occurred due to the offset value of the steering
torque.
[0066] Next, in a case of "with the correction by the offset correcting section", the simulation
results of the time responses of the steering angle and the steering torque will be
described. In this simulation, the gradient "a" in this offset countermeasure characteristic
is set to 0.1 [Nm/deg].
[0067] The simulation results are shown in FIGs.17A and 17B. The settings of the axes and
so on in FIGs.17A and 17B are the same as those in FIGs.16A and 16B. From FIG.17A,
the steering angle is slightly varied in the initial stage by performing the correction
at the offset correcting section. Then, it is understood that the steering angle balances
at 0.5 [deg] obtained by dividing the offset value 0.05 [Nm] by the gradient "a" (=
0.1 [Nm/deg]) and the handle is in the holding state. That is, the occurrence of the
assist due to the offset value of the steering torque is suppressed by the correction
at the offset correcting section.
[0068] Although the target steering torque generating section 200 according to the first
embodiment comprises the basic map section 210, the damper calculating section (including
the damper gain section 230 and the multiplying section 250) and the offset correcting
section 240, the target steering torque generating section 200 may treat only the
suppression of the assist occurrence due to the offset value of the steering torque,
and may comprise only the offset correcting section 240. The configuration example
of the target steering torque generating section in the above case (the second embodiment)
is shown in FIG.18. In the target steering torque generating section 600, the torque
signal Tref_c outputted from the offset correcting section 240 is outputted as the
target steering torque Tref. Moreover, the target steering torque generating section
may comprise the basic map section 210 and the offset correcting section 240 or may
comprise the damper calculating section and the offset correcting section 240.
[0069] The current command value which is calculated based on the steering torque in the
conventional EPS (hereinafter, referred to as "an assist current command value") may
be added to the motor current command value Imc outputted from the torsional angle
control section according to the first and second embodiments. For example, the current
command value Iref1 outputted from the current command value calculating section 31
shown in FIG.2, the current command value Iref2 in which the compensation signal CM
is added to the current command value Iref1, or the like may be added to the motor
current command value Imc.
[0070] In contrast with the first embodiment, the configuration example in which the above
function is included (the third embodiment) is shown in FIG.19. The assist control
section 700 comprises the current command value calculating section 31, or comprises
the current command value calculating section 31, the compensation signal generating
section 34 and the adding section 32A. The assist current command value lac outputted
from the assist control section 700 (corresponding to the current command value Iref1
or Iref2 in FIG.2) and the motor current command value Imc outputted from the torsional
angle control section 300 are added at an adding section 710 and the current command
value Ic which is the added result is inputted into the current limiting section 720.
The motor is driven based on the current command value Icm whose maximum current is
limited and the current control is performed.
[0071] In the first to the third embodiments, the phase compensating section 260 may be
provided at the previous stage of the basic map section 210 or the subsequent stage
of the basic map section 210 in the target steering torque generating section 200
including the basic map section 210. That is, the configuration of the region R surrounded
by the broken line in FIG.5 may be changed to the configuration shown in FIG.20A or
FIG.20B. The phase compensation at the phase compensating section 260 is set as the
phase lead compensation. For example, in a case that the phase lead compensation using
the primary filter in which the cutoff frequency of the numerator is set to 1.0 [Hz]
and the cutoff frequency of the denominator is set to 1.3 [Hz] is performed, the comfortable
steering feeling can be realized. If the target steering torque generating section
has the configuration based on the steering angle, its configuration is not limited
to the above configuration.
[0072] Further, in a case that the EPS control system is stable, the stabilization compensating
section may be omitted. The output limiting section can also be omitted.
[0073] In FIG.1 and FIG.3, although the present invention is applied to the column type
EPS, the present invention is not limited to an upstream-type EPS such as the column
type EPS, and can also be applied to a downstream-type EPS such as a rack and pinion
type EPS. Further, from a viewpoint of performing the feed-back control based on the
target torsional angle, the present invention can be applied to a steer-by-wire (SBW)
reaction force unit which comprises at least the torsion bar having any spring constant
and the sensor to detect the torsional angle. The embodiment (the fourth embodiment)
in which the present invention is applied to the SBW reaction force unit including
the torsion bar will be described.
[0074] First, the overall SBW system including the SBW reaction force unit will be described.
FIG.21 shows a configuration example of the SBW system, corresponding to the general
configuration of the electric power steering apparatus shown in FIG.1. The same reference
numerals designate the same components, and the detail explanation is omitted.
[0075] The SBW system does not have an intermediate shaft which is mechanically connected
to the column shaft 2 at the universal joint 4a and is a system that the operation
of the handle 1 is transmitted to the turning mechanism comprising the steered wheels
8L and 8R and so on by the electric signal. As shown in FIG.21, the SBW system comprises
the reaction force unit 60 and the driving unit 70, and the control unit (ECU) 50
controls the reaction force unit 60 and the driving unit 70. The reaction force unit
60 detects the steering angle θh by the steering angle sensor 14, and transmits the
motion state of the vehicle transmitted from the steered wheels 8L and 8R as the reaction
force torque to the driver. The reaction force torque is generated by the reaction
force motor 61. Although the SBW system which does not comprise the torsion bar in
the reaction force unit is existed, the SBW system which is applied to the present
invention comprises the torsion bar and the steering torque Ts is detected by the
torque sensor 10. The angle sensor 74 detects the motor angle θm of the reaction force
motor 61. The driving unit 70 drives the driving motor 71 in harmony with the steering
of the handle 1 by the driver. The driving force is applied to the pinion and rack
mechanism 5 via the gears 72 and turns the steered wheels 8L and 8R via the tie rods
6a and 6b. The angle sensor 73 is disposed in the vicinity of the pinion and rack
mechanism 5 and detects the turning angle θt of the steered wheels 8L and 8R. In order
to cooperative-control the reaction force unit 60 and the driving unit 70, the ECU
50 generates the voltage control command value Vref1 to drive and control the reaction
force motor 61 and the voltage control command value Vref2 to drive and control the
driving motor 71 based on the information of the steering angle θh, the turning angle
θt and so on outputted from the reaction force unit 60 and the driving unit 70, the
vehicle speed Vs detected at the vehicle speed sensor 12 or the like.
[0076] The configuration of the fourth embodiment that the present invention is applied
to such an SBW system will be described.
[0077] FIG.22 is a block diagram showing the configuration of the fourth embodiment. In
the fourth embodiment, the control to the torsional angle Δθ (hereinafter, referred
to as "the torsional angle control") and the control to the turning angle θt (hereinafter,
referred to as "the turning angle control") are performed. The reaction force unit
is controlled by the torsional angle control and the driving unit is controlled by
the turning angle control. The driving unit may be controlled by another control method.
[0078] In the torsional angle control, the configuration similar to that of the first embodiment
is used and the operation similar to that of the first embodiment is performed. The
control which follows-up the torsional angle Δθ to the target torsional angle Δθref
which is calculated through the target steering torque generating section 200 and
the converting section 400 by using the steering angle θh and so on, is performed.
The motor angle θm is detected by the angle sensor 74, and the motor angular velocity
com is calculated by differentiating the motor angle θm at the angular velocity calculating
section 951. The turning angle θt is detected by the angle sensor 73. Although the
detail explanation of the process in the EPS steering system/vehicle system 100 is
not described in the first embodiment, the current control section 130 has the configuration
similar to the combined configuration with the subtracting section 32B, the PI-control
section 35, the PWM-control section 36 and the inverter 37 shown in FIG.2, performs
the operation similar to that of the above combined sections, drives the reaction
force motor 61 based on the motor current command value Imc outputted from the torsional
angle control section 300 and the current value Imr of the reaction force motor 61
detected by the motor current detector 140, and performs the current control.
[0079] In the turning angle control, the target turning angle θtref is generated based on
the steering angle θh at the target turning angle generating section 910, the target
turning angle θtref and the turning angle θt are inputted into the turning angle control
section 920, and the turning angle control section 920 calculates the motor current
command value Imct so as to follow-up the turning angle θt to the target turning angle
θtref. The current control section 930 has the configuration similar to that of the
current control section 130, performs the operation similar to that of the current
control section 130, drives the driving motor 71 based on the motor current command
value Imct and the current value Imd of the driving motor 71 detected by the motor
current detector 940, and performs the current control.
[0080] The configuration example of the target turning angle generating section 910 is shown
in FIG.23. The target turning angle generating section 910 comprises a limiting section
931, a rate limiting section 932 and a correcting section 933.
[0081] The limiting section 931 limits the upper and lower limit values of the steering
angle θh and outputs the steering angle θh1. As well as the output limiting section
350 in the torsional control section 300, the upper limit value and the lower limit
value to the steering angle θh are preliminarily set, and the steering angle θh is
limited.
[0082] In order to avoid the sharp change of the steering angle, the rate limiting section
932 sets the limit value to the change amount of the steering angle θh1, limits the
change amount of the steering angle θh1 and outputs the steering angle θh2. For example,
the difference between the present steering angle θh1 and the steering angle θh1 prior
to one sampling is set as the change amount. In a case that the absolute value of
the change amount is larger than a predetermined value (the limit value), the addition
operation or the subtraction operation is performed to the steering angle θh1 so that
the absolute value of the change amount becomes the limit value, and the limited value
is outputted as the steering angle θh2. In a case that the absolute value of the change
amount is equal to or smaller than the limit value, the steering angle θh1 is outputted
as the steering angle θh2. Instead of setting the limit value to the absolute value
of the change amount, the change amount may be limited by setting the upper limit
value and the lower limit value to the change amount. Instead of limiting the change
amount, the limitation to the change rate or the difference rate may be performed.
[0083] The correcting section 933 corrects the steering angle θh2 and outputs the target
turning angle θtref. For example, similar to the basic map section 210 in the target
steering torque generating section 200, the target turning angle θtref is obtained
by the steering angle θh2 using the map that defines the characteristic of the target
turning angle θtref to the absolute value |θh2| of the steering angle θh2. Alternatively,
the target steering angle θtref may simply be calculated by multiplying the steering
angle θh2 by a predetermined gain.
[0084] A configuration example of the turning angle control section 920 is shown in FIG.24.
The turning angle control section 920 has a configuration similar to the configuration
example of the torsional angle control section 300 shown in FIG.11 excluding the stabilization
compensating section 340 and the adding section 362. Instead of the target torsional
angle Δθref and the torsional angle Δθ, the target turning angle θtref and the turning
angle θt are inputted into the turning angle control section 920. A turning steering
angle feed-back (FB) compensating section 921, a turning angular velocity calculating
section 922, the velocity control section 923, the output limiting section 926 and
the subtracting section 927 have the configuration similar to and are performed the
operation similar to those of the torsional angle FB compensating section 310, the
torsional angular velocity calculating section 320, the velocity control section 330,
the output limiting section 350 and the subtracting section 361, respectively.
[0085] In such a configuration, the operation example of the fourth embodiment will be described
with reference to the flowchart of FIG.25.
[0086] When the operation is started, the angle sensor 73 detects the turning angle θt and
the angle sensor 74 detects the motor angle θm (Step 5110). The turning angle θt is
inputted into the turning angle control section 920 and the motor angle θm is inputted
into the angular velocity calculating section 951.
[0087] The angular velocity calculating section 951 calculates the motor angular velocity
ωm by differentiating the motor angle θm and outputs the motor angular velocity com
to the right-turning/left-turning judging section 300 (Step S120).
[0088] Then, the similar operations from the Step S10 to the Step S50 shown in FIG. 13 are
performed, the reaction force motor 61 is driven, and the current control is performed
(Steps S130 to S170).
[0089] In the turning angle control, the target turning angle generating section 910 inputs
the steering angle θh and the steering angle θh is also inputted into the limiting
section 931. The limiting section 931 limits the upper and lower limit values of the
steering angle θh by using the preliminarily set upper and lower limit values (Step
S180), and outputs the limited value as the steering angle θh1 to the rate limiting
section 932. The rate limiting section 932 limits the change amount of the steering
angle θh1 by using a preliminarily set limit value (Step S190), and outputs the limited
value as the steering angle θh2 to the correcting section 933. The correcting section
933 corrects the steering angle 8h2, obtains the target turning angle θtref (Step
S200) and outputs the target turning angle θtref to the turning angle control section
920.
[0090] The turning angle control section 920 inputs the turning angle θt and the target
turning angle θtref and calculates a deviation Δθt
0 by subtracting the turning angle θt from the target turning angle θtref at the subtracting
section 927 (Step S210). The deviation Δθt
0 is inputted into the turning angle FB compensating section 921, and the turning angle
FB compensating section 921 compensates the deviation Δθt
0 by multiplying the deviation Δθt
0 by the compensation value (Step S220) and outputs the target turning angular velocity
ωtref to the velocity control section 923. The turning angular velocity calculating
section 922 inputs the turning angle θt, calculates the turning angular velocity ωtt
by differentiating the turning angle θt (Step S230) and outputs the turning angular
velocity ωtt to the velocity control section 923. The velocity control section 923
calculates the motor current command value Imcta by using the I-P control as well
as the operations of the velocity control section 330 (Step S240) and outputs the
motor current command value Imcta to the output limiting section 926. The output limiting
section 926 limits the upper and lower limit values of the motor current command value
Imcta by using the preliminarily set upper and lower limit values (Step S250) and
outputs the limited value as the motor current command value Imct (Step S260).
[0091] The motor current command value Imct is inputted into the current control section
930, and the current control section 930 drives the driving motor 71 based on the
motor current command value Imct and the current value Imd of the driving motor 71
which is detected by the motor current detector 940, and performs the current control
(Step S270).
[0092] The orders of inputting the data, the calculation and so on in FIG.25 are appropriately
changeable. As well as the velocity control section 330 in the torsional angle control
section, the velocity control section 923 in the turning angle control section 920
may use not the I-P control but the realizable control including at least one of the
P-control, the I-control and the D-control such as the PI-control, the P-control,
the PID control or the PI-D control. Further, the following-up control in the turning
angle control section 920 and the torsional angle control section 300 may be performed
by the generally used control configuration. With respect to the turning angle control
section 920, if the control configuration that the actual angle (the turning angle
θt in this case) follows-up the target angle (the target turning angle θtref in this
case) is employed, the control configuration is not limited to that of the apparatus
for the vehicle. For example, the control configuration which is used in an industrial
positioning apparatus, an industrial robot and so on may also be applied.
[0093] In the fourth embodiment, as shown in FIG.21, one ECU 50 controls the reaction force
unit 60 and the driving unit 70. The ECU for the reaction force unit 60 and the ECU
for the driving unit 70 may independently be provided. In this case, respective ECUs
transmit and receive the data by the communication. The SBW system shown in FIG.21
does not have a mechanical connection between the reaction force unit 60 and the driving
unit 70. The present invention is also applicable to the SBW system including the
mechanical torque transmission mechanism in which the column shaft 2 mechanically
connects to the turning mechanism via the clutch when the abnormality occurs in the
system. In such an SBW system, when the system operates in a normal state, the clutch
is off (disengaged) and the mechanical torque transmission is set to an open state.
When the abnormality occurs in the system, the clutch is on (engaged) and the mechanical
torque transmission is set to a usable state.
[0094] The torsional angle control section 300 in the first to the fourth embodiments and
the assist control section 700 in the third embodiment directly calculate the motor
current command value Imc and the assist current command value lac. Alternatively,
before calculating the motor current command value Imc and the assist current command
value lac, the expected motor torque (the target torque) is calculated and then the
motor current command value and the assist current command value may be calculated.
In this case, to obtain the motor current command value and the assist current command
value, the generally used relationship between the motor current and the motor torque
is utilized.
[0095] The drawings which are used in the explanation are a conceptual diagram for qualitatively
explaining the present invention, but the present invention is not limited to the
above drawings. While the above-described embodiments are examples of a preferable
embodiment of the present invention, the present invention is not limited thereto
and various modifications can be made without departing from the scope of the present
invention. The mechanism which is disposed between the handle and the motor or between
the handle and the reaction force motor and has any spring constant, may be used.
The above mechanism may not be limited to the torsion bar.
[0096] The main object of the present invention is to achieve the unit to obtain the target
steering torque for resolving the concern about the assist occurrence due to the offset
value of the steering torque. The unit to follow-up the steering torque to the target
steering torque may not be limited to the above-described unit including the converting
section and the torsional angle control section.
Explanation of Reference Numerals
[0097]
- 1
- handle
- 2
- column shaft (steering shaft, handle shaft)
- 2A
- torsion bar
- 3
- reduction mechanism
- 10
- torque sensor
- 12
- vehicle speed sensor
- 14
- steering angle sensor
- 20
- motor
- 30, 50
- control unit (ECU)
- 31
- current command value calculating section
- 33, 720
- current limiting section
- 34
- compensation signal generating section
- 38, 140, 940
- motor current detector
- 60
- reaction force unit
- 61
- reaction force motor
- 70
- driving unit
- 71
- driving motor
- 72
- gears
- 73, 74
- angle sensor
- 100
- EPS steering system/vehicle system
- 130, 930
- current control section
- 200, 600
- target steering torque generating section
- 210
- basic map section
- 230
- damper gain section
- 240
- offset correcting section
- 241
- offset correction calculating section
- 242
- vehicle speed sensitive gain section
- 260
- phase compensating section
- 300
- torsional angle control section
- 310
- torsional angle feed-back (FB) compensating section
- 320
- torsional angular velocity calculating section
- 330, 923
- velocity control section
- 340
- stabilization compensating section
- 350, 926
- output limiting section
- 400
- converting section
- 500
- right-turning/left-turning judging section
- 700
- assist control section
- 910
- target turning angle generating section
- 920
- turning angle control section
- 921
- turning angle feed-back (FB) compensating section
- 922
- turning angular velocity calculating section
- 931
- limiting section
- 932
- rate limiting section
- 933
- correcting section
- 951
- angular velocity calculating section